Nanostructured Metal Oxides as Cathode Interfacial Layers for Hybrid-Polymer Electronic Devices

We report the use of nanostructured metal oxides as cathode interfacial layers for improved performance hybrid polymer electronic devices such as light-emitting diodes (PLEDs) and solar cells. In particular, we employ a stoichiometric (WO3) and a partially reduced tungsten metal oxide (WOx) (x<3), both deposited as very thin layers between an aluminum (Al) cathode and the active polymer layer in hybrid PLEDs and achieve improved PLED device performance reflected as an increase in the current density and luminance and a reduction of the operating voltage. On the other hand, we investigate the use of a stoichiometric tungsten oxide layer as a thin cathode interfacial layer in hybrid polymer photovoltaic cells (Hy-PVs). We demonstrate improved photovoltaic cell performance, primarily as a result of the substantial increase in the short-circuit photocurrent. The improved PLED device characteristics are attributed to enhanced electron injection that primarily results from the lowering of the effective interfacial barrier, as evidenced by photovoltaic open circuit voltage measurements, and improved electron transfer. On the other hand, the observed improvement in the hybrid solar cell performance is primarily attributed to its enhanced internal quantum efficiency, most likely due to the improved electron transport and extraction at the active layer/WO3/Al interface and the reduction of the corresponding contact series resistance. Correlation between the metal oxide surface morphology and the device performance is also investigated and will be discussed.